(CNN) -- Could reliability be an Achilles heel for Formula One world champions Red Bull this season? If the first two days of winter testing are anything to go by the answer could be yes.
Four-time world champion Sebastian Vettel was stopped in his tracks by an engine failure after completing just eight laps in the new Red Bull racer Wednesday.
"We've not had a lot of running and have a few problems to sort out," Vettel told reporters at the Jerez circuit in Spain. "But with such big rule changes it is usual to have some teething problems.
"That's what tests are for, to sort those issues out. The next two days will be important to get some track time to prepare for the tests in Bahrain."
Vettel, who only managed three laps in the box fresh car on Tuesday, has now returned home to Switzerland and handed the keys of the 2014 Red Bull over to his new teammate Daniel Ricciardo for the remainder of the Jerez test.
Preseason testing is always a tense time but a major rule change has heaped extra pressure on the teams hoping to get their cars race ready for the opening Australian Grand Prix on March 16.
The cars are now powered by 1.6-liter V6 turbo engines which also rely on a greater use of hybrid energy -- recovered through braking and from the car's exhaust gases.
Although engine suppliers Renault, Ferrari and Mercedes put their engines through their paces on dynamometers at their headquarters, they are running them on the cars for the first time this week.
Red Bull, who along with the Lotus and Caterham teams use Renault engines, had to cut short Vettel's track time because of problem with the energy recovery system on his car.
Engine gremlins also affected Toro Rosso, Red Bull's sister team, and driver Daniil Kvyat was not able to take his car out on track because of an electrical problem.
McLaren recovered from the technical issues that had kept its car in the garage Tuesday to see Jenson Button set the leading time in its 2014 racer with a best lap of one minute 24.165 seconds among 44 laps overall.
"For our first day of actual running, we were able to get a good understanding of the car, and the way the engine and turbo behaves," Button told reporters. "It's tricky, and very different to what we're used to, but I feel that these cars will be enjoyable to drive."
On Wednesday, McLaren also announced former Lotus team principal Eric Boullier as its new racing director as a restructure of the team continues.
It was another solid day from Ferrari's Kimi Raikkonen, who set the second fastest time ahead of Valtteri Bottas in the Williams and Nico Rosberg's Mercedes.
Rosberg underlined Mercedes' reliability by ticking off 96 laps, all the more impressive as the car had to rebuilt over night following Lewis Hamilton's crash on the opening day of the test.